Despite recent advances in treating ischemic injuries, stroke and myocardial infarction continue to kill or disable vast numbers of people each year. In the United States alone, 600,000 new myocardial infarctions and 320,000 recurrent attacks occur annually. About 38 percent of the people who experience a myocardial infarction in a given year will die, while many of those who survive will experience some loss in cardiac function.
Certain cell types, including muscle cells and neurons are particularly vulnerable to ischemic injury in connection with myocardial infarction and stroke. Technologies associated with the identification, isolation, and culture of stem/progenitor cells now provides many candidate cells for cell replacement applications in regenerative medicine. Notably, however, transplantation of culture-expanded adult stem/progenitor cells often results in poor cellular engraftment, survival, and migration into sites of tissue injury. As such, current cell replacement strategies for treating myocardial infarction involving the injection of stem/progenitor cells result in modest improvements in cardiac function, at best. Low levels of engraftment, survival, and cell replacement after injection of adult or embryonic stem cells into the injured left ventricle wall are important issues that reduce the potential effectiveness of cell replacement strategies after myocardial infarction. Moreover, intravenous infusion of cultured adult stem/progenitor cells can be accompanied by microembolism and cardiac arrhythmias. Accordingly, improved methods of treating tissue injury, particularly ischemic injuries associated with myocardial infarction, are urgently required.